In industry in general and more particularly in the press machine art, considerably greater emphasis is being laid on safety and on the prevention of injury to the machine operator. Thus, safety systems are provided which require that the operator hold switches closed during the descent of the press ram. This requirement ensures that the operator's hands are away from the area beneath ram or the ram cannot descend. An example of a mechanical block of this type is shown in U.S. Pat. No. 3,999,477 to Good.
Other patents are known showing a pressure cushion acting as a hydraulic overload safety device for counterbalancing the weight of the ram, i.e., U.S. Pat. No. 4,011,809 issued Mar. 15, 1977 to E. Waller et al issued Mar. 15, 1977.